Population GrowthPopulation Growth

Factors that regulate population Factors that regulate population sizesize

Population Growth PatternsPopulation Growth Patterns• Population CharacteristicsPopulation Characteristics

– SizeSize– DensityDensity

•number per areanumber per area

– DistributionDistribution•UniformUniform

•RandomRandom

•ClumpedClumped

Population Distributions

Random

Uniform

Clumped

Population CharacteristicsPopulation Characteristics– Sex ratiosSex ratios

– Age structureAge structure

•Number of individuals in different age Number of individuals in different age

classesclasses

– Reproductive ageReproductive age

– Pre-reproductive agePre-reproductive age

– Post-reproductive agePost-reproductive age

Age Structure Diagrams

Population GrowthPopulation Growth•Growth RateGrowth Rate

– Factors that increase population sizesFactors that increase population sizes•Birth Rate (BR)Birth Rate (BR)•Immigration (Im)Immigration (Im)

– Factors that decrease population sizesFactors that decrease population sizes•Death Rate (DR)Death Rate (DR)•Emigration (Em)Emigration (Em)

Growth Rate = (BR + ImR) – (DR + EmR)Growth Rate = (BR + ImR) – (DR + EmR)

• Exponential growthExponential growth– A stable rate of growth leads to A stable rate of growth leads to

exponential growth.exponential growth.– As the population size increases, the As the population size increases, the

same percentage increase becomes a same percentage increase becomes a larger total increase.larger total increase.

Exponential Growth in a population

J-curve

Occurs when a population starts out small and environmental conditions are ideal.

• Factors that limit GrowthFactors that limit Growth– Physical, chemical and biological factors Physical, chemical and biological factors

(biotic and abiotic) that limit the amount (biotic and abiotic) that limit the amount of growth of growth •SpaceSpace

•NutrientsNutrients

•PredatorsPredators

– All limiting factors together make up the All limiting factors together make up the “environmental resistance” and affect “environmental resistance” and affect the carrying capacity of the the carrying capacity of the environmentenvironment

Logistic Growth Curve (S-curve)

Environmental Resistance determines Carrying Capacity

Carrying Capacity can change when limiting factors change

Limiting FactorsLimiting Factors

• Shelford’s Law of Tolerance (p. 588)Shelford’s Law of Tolerance (p. 588)– Certain range of environmental Certain range of environmental

conditions that will allow for maximum conditions that will allow for maximum population growthpopulation growth

• Density Independent factors affect a Density Independent factors affect a population regardless of its sizepopulation regardless of its size– Abiotic factors: climate, spaceAbiotic factors: climate, space

Limiting FactorsLimiting Factors

• Density dependent factorsDensity dependent factors– Population size can limit further Population size can limit further

population growthpopulation growth– Intraspecific competitionIntraspecific competition

•Food resourcesFood resources•MatesMates

– Disease Disease – Interspecific CompetitionInterspecific Competition– PredationPredation

DemographyDemography

• The study of human populationsThe study of human populations

– Population SizePopulation Size

– Population Density and DistributionPopulation Density and Distribution

– Age StructureAge Structure

– Sex RatiosSex Ratios

Human Population GrowthHuman Population Growth

• Human population growth has been Human population growth has been greater than exponential.greater than exponential.

– Growth rate has increased over time Growth rate has increased over time (mostly because of lower death rates).(mostly because of lower death rates).

– Global growth rate peaked at 2.1% in Global growth rate peaked at 2.1% in the 1960’s.the 1960’s.

Global Human Population

Human DistributionHuman Distribution

Effect of Age Structure on Population Effect of Age Structure on Population GrowthGrowth

Age Structure Diagrams

Age Pyramid for United StatesAge Pyramid for United States

Age structures are very different Age structures are very different in the developed and developing in the developed and developing countriescountries

Effect of sex ratios on population Effect of sex ratios on population growthgrowth

What is the earth’s carrying What is the earth’s carrying capacity?capacity?• Carrying capacity is influenced by, Carrying capacity is influenced by,

but not defined by, environmental but not defined by, environmental impact.impact.

• Environmental impact depends on Environmental impact depends on more than population alone.more than population alone.

– Technology can increase or decrease Technology can increase or decrease the impact.the impact.•Cause more consumption – or – Cause more consumption – or –

•Exploit previously unavailable resourcesExploit previously unavailable resources

Technological innovations that increased carrying capacity

Decline in Global Growth RateDecline in Global Growth Rate

Is growth rate responding to Is growth rate responding to environmental resistance? environmental resistance?

• What part of the growth rate What part of the growth rate equation is changing?equation is changing?

• Is the change occurring fastest where Is the change occurring fastest where resources are scarcest?resources are scarcest?

• Is the change resulting in less Is the change resulting in less environmental impact?environmental impact?

TFR correlates with social TFR correlates with social opportunity for womenopportunity for women

Growth rates are unevenly distributed

Population is increasing fastest Population is increasing fastest where the standard of living is where the standard of living is lowestlowest

Ecological FootprintsEcological Footprints

The amount of resources used per person can be expressed in terms of the amount of land needed to provide those resources

What does the future hold?